I keep coming across small design differences that were implemented by Lotus and thought they would be interesting to share on this thread.
To kick off, lets look at the rear hatch window. I've known for a while that the earliest cars had alloy hinges, that were changed to Chrome plated steel certainly before 1976, but recently spotted following on the Anodized surround trim.

74 model on the left, 76 model on the right. Note increased horizontal on top corner (hides joint under the hinge), the different radius to the lower corner, and one you can't really see on the photo, but the inner corner trim is simple flat plate on the 74 car, but 3 dimensional (dished) on the later car. - No wonder you couldn't keep water out of the boot !!!

All : feel free to add "continuous improvements" you may come across. I have a few others I know of which I'll post in due course
Tony